fix(player): 使用雪碧图预热首帧兜底

lib/pages/player/widgets/player_video_surface.dart

@@ -18,6 +18,7 @@ class PlayerVideoSurface extends StatefulWidget {
     required this.theater,
     this.handoff,
     this.openingFrame,
+    this.openingFrameReady = false,
     this.holdOpeningUntilFirstFrame = false,
     this.preparedFrameAvailable = false,
   });
@@ -28,6 +29,9 @@ class PlayerVideoSurface extends StatefulWidget {
   /// 解码出第一帧之前垫上的视频首帧，没有则为空。
   final Widget? openingFrame;
 
+  /// 当前集雪碧图 t=0 是否已在共享缓存中可用。
+  final bool openingFrameReady;
+
   /// 播放中的新片源在位置首次前进前继续显示封面，避免混入未出帧纹理。
   final bool holdOpeningUntilFirstFrame;
 
@@ -73,10 +77,10 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
     final controller = widget.controller;
     final handoff = _liveHandoff(controller);
     final firstFrameSeen = _trackFrameState(controller, value);
-    final firstFrameReady =
-        widget.preparedFrameAvailable || firstFrameSeen;
+    final firstFrameReady = widget.preparedFrameAvailable || firstFrameSeen;
     final textureReady = _shouldReveal(value, handoff != null);
-    final reveal = textureReady &&
+    final reveal =
+        textureReady &&
         (!widget.holdOpeningUntilFirstFrame ||
             widget.preparedFrameAvailable ||
             firstFrameReady ||
@@ -86,13 +90,7 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
     final showOpening =
         widget.openingFrame != null && handoff == null && !reveal;
     _logStateChange(value);
-    _logLayerState(
-      value,
-      handoff,
-      reveal,
-      firstFrameReady,
-      showOpening,
-    );
+    _logLayerState(value, handoff, reveal, firstFrameReady, showOpening);
     return Stack(
       fit: StackFit.expand,
       children: [
@@ -203,10 +201,20 @@ class _PlayerVideoSurfaceState extends State<PlayerVideoSurface> {
         : !firstFrameReady && widget.holdOpeningUntilFirstFrame
         ? 'awaiting-first-frame'
         : 'reveal';
+    final fallback = handoff != null
+        ? 'handoff'
+        : showOpening
+        ? widget.openingFrameReady
+              ? 'thumbnails-first-frame'
+              : 'black'
+        : reveal
+        ? 'video'
+        : 'black';
     final signature =
         'warm=${widget.preparedFrameAvailable ? 1 : 0} '
         'frame=${firstFrameReady ? 1 : 0} '
-        'cover=${showOpening ? 1 : 0} '
+        'thumbnails=${widget.openingFrameReady ? 'ready' : 'pending'} '
+        'fallback=$fallback '
         'video=${reveal ? 1 : 0} handoff=${handoff == null ? 0 : 1} '
         'init=${value?.isInitialized == true ? 1 : 0} '
         'playing=${value?.isPlaying == true ? 1 : 0} '